October 1st 2012
The types in TypeScript are annotations: an optional way of recording and enforcing types. The compiler will give you compiletime warnings when calling a function with an incorrect signature for example.
TypeScript also supports interfaces, classes (the same syntax as currently proposed by the next version of EcmaScript), modules, file importing, public and private data, and probably more. The documentation appears to be a little lacking at the moment, but you can check out a quickstart guide, some sample source code, and of course the source code of the compiler itself on Microsoft’s source code website.
Here is a video of Anders Hejlsberg, the author of the language at Microsoft introducing TypeScript.